1. Field of the Invention
The present invention relates to a color display tube and a color display tube device used for example in a television or a computer display.
2. Description of Related Art
A cathode ray tube including an in-line color display tube generally has a cylindrical glass neck portion that surrounds an electron gun and is connected to a cone portion that flares like a bell from the neck portion toward a screen of a front panel. A region from the neck portion toward the cone portion is provided with a deflection yoke for deflecting an electron beam emitted from the electron gun.
A deflection power P, which is an electric power consumption of the deflection yoke, is proportional to a diameter Da of the neck portion and a diameter Dc of a ferrite core in the deflection yoke, as indicated by the following equation.
P=kxc2x7Daxc2x7Dcxc2x7sin2(xcex1/2)L
k: constant, xcex1: deflection angle, L: deflection length
In other words, a smaller neck diameter linearly brings about a smaller deflection power, thereby saving electric power.
However, when the neck diameter is reduced, a main lens aperture of the electron gun also decreases. Since the diameter of a beam spot is proportional to the xe2x89xa6xc2xe power of the main lens aperture, the smaller neck diameter leads to an increase in the beam spot diameter. This is disadvantageous in achieving high resolution.
Thus, the electric power saving achieved by the smaller neck diameter and the high resolution cannot be obtained at the same time. In a mainstream color display tube, an improved electron gun has been under development in order to achieve the high resolution while keeping a constant neck diameter Da of 29.1 mm.
On the other hand, one of the cathode ray tubes is a miniature cathode ray tube for a viewfinder in a video camera, in which a two-stage neck diameter Da has been suggested and produced commercially as a technology to achieve the electric power saving and the high resolution at the same time with respect to the neck diameter (for example, JP 3(1991)-192636 A, and National Technical Report Vol. 38, No. 4, August 1992, pages 408-415). In this technology, the neck diameter is extended in the electron gun region where the main lens is located, while the neck diameter is reduced in the region where the deflection yoke is mounted.
However, in this conventional two-stage neck diameter Da, the deflection yoke has to be assembled directly in the cathode ray tube because physical limitations make it impossible to attach the normally-produced deflection yoke to and remove it from the cathode ray tube. This has posed a serious problem in productivity. This is because the deflection yoke that matches the two-stage neck diameter has an inner diameter having a portion smaller than the neck diameter in the rear end of the cathode ray tube, and the neck portion, therefore, cannot be inserted in the deflection yoke.
In other words, when the deflection yoke is assembled directly in the cathode ray tube during its manufacture, the degree of freedom in assembly is smaller and the productivity is lower than the case of manufacturing the deflection yoke separately. In addition, assembly jigs cannot be introduced optimally, making it difficult to maintain a high quality. Furthermore, it is impossible to spot defective products individually with respect to the cathode ray tubes and the deflection yokes, leading to serious problems such as high cost of quality loss. Thus, the cathode ray tube with the two-stage neck diameter Da so far has not led to a commercialization in a color display tube device used in a television, a computer display or the like, other than in the actual example of the miniature cathode ray tube for the viewfinder described above.
It is an object of the present invention to solve the problems described above and to provide a color display tube and a color display tube device that can achieve both an electric power saving and a high resolution easily without lowering productivity or quality.
In order to achieve the object mentioned above, a color display tube according to the present invention includes an envelope including a front panel and a funnel, and an electron gun provided in a neck portion of the funnel. A horizontal outer diameter of the neck portion in a region on a rear end side is greater than a vertical outer diameter thereof in this region and a horizontal outer diameter thereof in a region on the front panel side. A main lens of the electron gun is formed in the region on the rear end side.
Also, a color display tube device of the present invention includes the above-described color display tube, and a deflection yoke arranged so that a rear end of horizontal deflection coils is located in the region on the front panel side of the neck portion. A horizontal inner diameter of the rear end of the horizontal deflection coils of the deflection yoke is greater than the vertical outer diameter of the neck portion in the region on the rear end side. A vertical inner diameter of the rear end of the horizontal deflection coils is greater than the horizontal outer diameter of the neck portion in the region on the rear end side.
According to the color display tube and the color display tube device of the present invention, it is possible to achieve both the electric power saving and the high resolution easily without lowering productivity or quality.
In the above color display tube device, it is preferable that the horizontal inner diameter of the rear end of the horizontal deflection coils of the deflection yoke is smaller than the horizontal outer diameter of the neck portion in the region on the rear end side. This makes it possible to reduce a horizontal deflection power, thereby further saving the electric power.